What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting?

  What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting? The size of tremie pipe is about 300mm with sections having flange couplings fitted with gasket to prevent water leakage. The tremie pipe should be closed initially to prevent water from entering the pipe. It should be designed with sufficient thickness and weight so that it would not be buoyant when empty inside water. The placement of tremie concrete is commenced by putting the closed pipe underwater to the location for concreting, followed by partial filling of tremie pipe with concrete. In order to have tremie concrete flowed out of the pipe, it is necessary to fill the pipe with concrete of sufficient height to overcome the water pressure and frictional head. After that the tremie pipe is raised about 150mm to allow concrete to flow out. To enhance sufficient bonding, each succeeding layer of concrete should be placed before the preceding layer has reached
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WHAT IS ESTIMATION IN CONSTRUCTION ??? WHAT ARE THE DIFFERENT TYPE OF ESTIMATES USED IN CONSTRUCTION???

WHAT IS ESTIMATION

Before commencement of any work it is necessary that estimates are prepared for the purpose of obtaining technical sanction/ financial concurrence/ administrative approval,

 TYPE OF ESTIMATE USED IN CONSTRUCTION

        i)  Preliminary Estimates

        ii)   Detailed Estimates

Preliminary Estimates:

It is necessary to know the financial implications of a proposed work before it is taken up and so a preliminary estimate is prepared for the purpose based on a draft scheme of the proposed work. The preliminary estimate is the basis for seeking administrative approval and it is often prepared on prorata basis based on cost of similar work done in past or on rough estimate/ thumb rule basis. For building works this may be based on cost per unit area or per unit volume of covered space. For haul road, this may be cost per kilometer. Preliminary estimates may be based on similar works executed in the past.

 Important point for preliminary estimate:

 a)   Approx. and feasible cost (of a building for example) on broad basis but with due regard to foundation and drainage problem, architectural and structural requirements, cost expected due to local special condition, special construction method and technique etc. which should be supported by a proper report.

b)  Approx., cost required for architecture and engineering and interior and landscape designs.

c)   Approx., cost of interior furnishing, electrical installations, meeting the requirements of Building Bye-laws of local bodies.

d)  For industrial structures 10% extra is to be added to the estimated cost derived on the basis of prevalent SOR

e)  For underground works estimate is to be prepared on analysis based on wage board rates for labour component, prevalent material cost and working conditions.

 f)   In every estimates, a provision of 3% shall be made for contingent expenditure, which will be controlled by CGM(C)/ GM(C) who will use this fund on meeting all urgent and miscellaneous items including temporary structures and purchase/ hiring of vehicles and other adjunct services required for effective supervision and control of the works. CGM(C)/ GM(C) can at his discretion delegate this power to the subordinate officer.

     Detailed Estimates :

 In general the detailed site investigation and preparation of plans, designs and estimates for a work should not be taken up unless the administrative approval has been obtained or the work is included in the proposed budget. For preparation of the detailed estimates, the site investigation along with subsoil exploration, whenever required, is necessary for proper design of foundations and for arriving at realistic cost estimates to avoid changes during execution warranting revised estimates. The detailed estimates shall be prepared based on current/-updated schedule of rates (SOR). For the items of work not covered by the SOR, analysis of the rates shall be prepared based on market rates of materials and labour and these are to be incorporated separately in the estimate.

 All detailed estimates should consist of:

 i)  A report covering a brief description of the project and Budget Provision & Allocation.

 ii)  Design and Drawings.

 iii)   Scope of Work

 iv)  Rates

 v)  Detailed estimates of the quantities with detailed statement of measurements.

 vi)  Analysis of rates for non-schedule items

 vii)  Abstract of cost indicating value of work based on SOR and analysed rates.

 viii)  Method of execution

 ix)  Requirement of important materials, special T&P.

 x)  Requirement of labour

 xi)  Availability of clear working site.

 xii)  Brief Specifications

 xiii)  Deviation from approved/ standard norms & justification thereof, in regard to areas, specifications, amenities etc.

 xiv)  Soil report, wherever required

 xv)  Period of execution

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